Hedge-fund star Larry Robbins has made a big bet on hospitals and is pushing them a little harder to buy back stock or make acquisitions. Why he's taking on HMA.

Larry Robbins usually describes the approach of his $6.4 billion hedge-fund firm, Glenview Capital Management, as "suggestivist," cultivating amicable working relationships with corporate management to propose shareholder-friendly changes. Now he's becoming an activist for the first time, challenging one of his holdings in a proxy contest that is under way.